Methods of objectively evaluating image quality of videos include methods of using the absolute difference, squared difference, and S/N ratio of pixel values (luminance, a color difference, an RGB value, etc.) between an original image and an image of interest for evaluation. For example, an image quality evaluation method disclosed in Patent Document 1 uses the S/N ratio while taking account of human visual properties varying with the spatial frequency, and determines an objective image quality value by calculating an S/N ratio based on a differential value between a pixel value of data of an image of interest for evaluation and that of its original image, and applying a weight to the S/N ratio based on the power of the alternating-current components for the image data in a whole frame.
The image quality evaluation method as disclosed in Patent Document 1, however, does not take account of visual properties with respect to a change in video signals in a temporal direction, and therefore, the correlation with the result of actual subjective evaluation is not always high.
Another image quality evaluation method is disclosed in Patent Document 2. The image quality evaluation method as disclosed in Patent Document 2 determines, for example, a difference in pixel value between consecutive frames on a pixel-by-pixel basis, and applying weighting processing to the S/N ratio based on the magnitude of the difference.
Patent Document 1: JP-3458600B2
Patent Document 2: JP-P2007-110189A